Since the thicknesses of semiconductor devices tend to be reduced, during a procedure employed in the manufacture of wafers for these devices, a thickness reduction process is performed to reduce the thicknesses of substrates. As part of this thickness reduction process, a circuit pattern is formed on one surface of a silicon substrate and the opposite face is mechanically ground. Following the grinding, a plasma process is used to remove a damaged layer, using etching, from the face of the silicon substrate for which the machine grinding was performed.
Since wafers come in a variety of sizes, it is desirable that a single plasma processing apparatus for performing such a wafer plasma process be capable of handling wafers having different sizes. Consequently, presently well known plasma processing apparatuses were developed for which part or all of an electrode whereon a wafer is positioned can be replaced, depending on the size of the wafer that is to be processed (see, for example, patent documents 1 and 2). According to the example in patent document 1, an electrode is composed of a plurality of layers, and only the topmost layer, on which a wafer to be processed is positioned, is replaced. According to the example in patent document 2, an entire electrode member, through which cooling water channels are formed, is replaced.
[Patent Document 1] JP-A-10-223725
[Patent Document 2] JP-A-2001-210622
However, the plasma processing apparatuses disclosed in these conventional examples have the following problems. First, during the plasma process, an electrode must be appropriately cooled in order to prevent an excessive rise in the temperature of the electrode or of a wafer that is heated by plasma. However, since according to the example in patent document 1 an electrode is divided into layers, thermal conduction is blocked at the joint where the portion of an electrode that is replaced contacts the portion that is not replaced, and a reduction in the cooling efficiency is unavoidable.
According to the example in patent document 2, since an expensive electrode member must be fabricated that corresponds in size to a wafer, costs is increased. In addition, since the space available for the removal and mounting of electrode members is limited, the work efficiency for the replacement of an electrode is low; excessive labor and time are required. Furthermore, during a replacement operation, cooling water retained in an electrode tends to leak into a processing chamber, which is a frequent cause of contamination. As is described above, conventionally, it is difficult to easily and inexpensively process a plurality of wafers having different sizes using a single plasma processing apparatus.